1. Field of the Invention
The present invention relates generally to passive infrared (PIR) motion sensors, and is particularly concerned with a PIR motion sensor system and method which includes a target.
2. Related Art
Passive infrared motion sensors generally consist of several features. An optical element (such as a lens or mirror) and an infrared (IR) detector together define and collect radiation from a field-of-view (intersecting and thus defining a monitored spatial volume), from which the optical element conveys radiation onto an infrared (IR) detector which is generally responsive to mid-IR light in the 6-14 micron wavelength range. The detector, in turn, provides an electrical signal responsive to changes in the effective blackbody temperature of the surfaces of objects within the monitored volume and radiating toward the optical element, which signal is passed to analog processing circuits, which, in turn, create a digital signal that may be directly or indirectly compared to a certain threshold amount of temperature change “seen” by the optical element from within the monitored volume. The digital signal may be further processed by logic circuits in order to provide a desired output indication, for example, of a warmer human crossing in front of cooler objects or background within a monitored volume.
One type of prior art infrared motion sensor system is illustrated in FIG. 1 and comprises an active-beam sensor system in which a pulsed, near-infrared (NIR) light beam is transmitted from transmitter 10 to receiver 12. Each transmitter has an emitter 15 and a lens 16 for directing the NIR light beam towards the receiver. Each receiver has a lens 17 and a detector 18 for receiving light directed by the lens onto the detector. A processor associated with the detector is configured to confirm NIR light transmission through the monitored volume 14 between transmitter 10 and receiver 12. The volume is typically a cylinder of 3 to 10 cm. diameter. Transmission interruption indicates objects moving within the monitored volume. Such active-beam sensors are commonly employed to monitor a facility's perimeter, by installing multiple transmitter/receiver linear segments in different directions so as to form a complete “fence” around the facility. The monitored volume in such systems is much less than human size so that the detector may be triggered by moving objects much smaller than humans.
Another known type of infrared motion sensor is a conventional long-range passive infrared (FIR) sensor 20 as illustrated in FIG. 2. This type of sensor monitors long and narrow static volumes 22, as indicated in FIG. 2, and has an infrared detector 24 and an optical element such as lens 25 which conveys radiation received from the monitored volume onto the detector. Such sensors are often employed to monitor a facility's perimeter by installing multiple PIR sensors whose monitored volumes form linear segments in different directions, so as to form a complete “fence” around the facility. One problem with this type of system is that the detection range cannot be controlled accurately, and will vary widely in response to different temperature, air clarity and other conditions which affect the detected temperature difference between a detected moving body and the background.